Mgo board(magnesium oxychloride hydrate) corrode steel,Why?

Mgo board(magnesium oxychloride hydrate) corrode steel,Why?

Metallic corrosion is the process of either stealing or donating electrons, when the electrons are stolen or donated, the metal atoms will dissolve in the water. Salt water is a the main conductor, so the rate of corrosion increases dramatically. When mgo board in high humidty enviroment(80%),inside chloride iron will dissolve and move toward water,when it contact with metal,unavoidale corrosion will happen on its surface.